Abstract
To improve the electrical performance and bias-stress stability of amorphous InGaZnO thin-film transistors (a-IGZO TFTs), we fabricated and characterized buried-channel devices with multiple-stacked channel layers, i.e., a nitrogen-doped a-IGZO film (front-channel layer), a conventional a-IGZO film (buried-channel layer), and a nitrogen-doped a-IGZO film (back-channel layer). The larger field-effect mobility (5.8 cm2V−1s−1), the smaller subthreshold swing value (0.8 V/dec, and the better stability (smaller threshold voltage shifts during bias-stress and light illumination tests) were obtained for the buried-channel device relative to the conventional a-IGZO TFT. The specially designed channel-layer structure resulted in multiple conduction channels and hence large field-effect mobility. The in situ nitrogen-doping caused reductions in both the front-channel interface trap density and the density of deep states in the bulk channel layers, leading to a small subthreshold swing value. The better stability properties may be related to both the reduced trap states by nitrogen-doping and the passivation effect of the nitrogen-doped a-IGZO films at the device back channels.
Highlights
Amorphous silicon thin-film transistors (a-Si TFTs) are the mainstream of active-matrix devices for flat panel displays (FPDs); polycrystalline (p-Si) TFTs are used to address some high-standard FPD products
Some researchers— including our group—reported that nitrogen-doping (N-doping) effectively improved the electrical properties (e.g., subthreshold swing (SS) and bias-stress stability) of amorphous InGaZnO (a-IGZO) TFTs by decreasing the number of deep states and oxygen vacancies (Vo) in the device channel layers and reducing the channel/dielectric interface trap density with N atoms incorporated into the a-IGZO film [6,7,8]
The a-IGZO:N film used as the front-channel layer in the buried-channel structure could reduce both the interface trap density and the bulk-layer deep state density, leading to a smaller SS value (0.8 V/dec) in comparison with the conventional a-IGZO TFT device (SS = 1.3 V/dec)
Summary
Some researchers— including our group—reported that nitrogen-doping (N-doping) effectively improved the electrical properties (e.g., subthreshold swing (SS) and bias-stress stability) of a-IGZO TFTs by decreasing the number of deep states and oxygen vacancies (Vo) in the device channel layers and reducing the channel/dielectric interface trap density with N atoms incorporated into the a-IGZO film [6,7,8]. In this study, buried-channel a-IGZO:N TFTs, i.e., devices with multiple-stacked channel layers, were fabricated and evaluated These devices showed better performance and stability than the Micromachines 2019, 10, 779. These devices showed better performance and stability than the ccoonnventional devices. SiOx (100 nm) p++ Si a-IGZO:N (30 nm) SiOx (100 nm) p++ Si a-IGZO:N (10 nm) a-IGZO (10 nm) a-IGZO:N (10 nm)
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